CN117177774A - Covalent conjugates of SARS-COV-2 receptor binding domain and carrier protein and vaccine compositions comprising the same - Google Patents

Abstract

The present invention relates to biotechnology, and more particularly to the field of human health. The invention particularly describes conjugates of SARS-CoV-2 receptor binding domain covalently conjugated to a carrier protein, methods for obtaining them, and vaccine compositions comprising them. The vaccine compositions described in the present invention are useful for preventing SARS-CoV-2 infection because they induce a strong neutralizing antibody response.

Description

Covalent conjugates of SARS-COV-2 receptor binding domain and carrier protein and vaccine compositions comprising the same

Technical Field

The present invention relates to biotechnology, and more particularly to the field of human health. The invention specifically describes covalent conjugates of SARS-CoV-2 receptor binding domain and carrier protein, methods for obtaining them, and vaccine compositions comprising them.

Background

Covd-19 is a very new disease, found in month 12 of 2019, when severe cases of pneumonia of unknown etiology began to be reported. Diseases caused by the SARS-CoV-2 virus are characterized by rapid spread and the appearance of symptoms such as fever, cough, runny nose, sore throat, and dyspnea in symptomatic patients, such patients accounting for less than 50%. The remainder of the people who are infected with the disease are asymptomatic, a key factor in viral transmission, representing an epidemiological challenge in their control.

Other coronaviruses like SARS-CoV-2 (known as MERS and SARS) have caused similar epidemics over the last decades. SARS shows greater homology with SARS-CoV-2, one of the main similarities between them being that both viruses use the ACE2 protein as receptor to enter human cells. Thus, in SARS and SARS-CoV-2, the interaction between the Receptor Binding Domain (RBD) of the S1 viral protein and the ACE2 (angiotensin converting enzyme 2) protein is a determining factor in human infection with the virus. (Walls A et al (2020) Cell https:// doi.org/10.1016/j.cell.2020.02.058). The RBD of the S protein of SARS-CoV-2 is an approximately 195 amino acid fragment (sequences 333-257) that contains the Receptor Binding Motif (RBM), a region where the virus interacts with the ACE2 receptor. RBD contains 4 intramolecular disulfide bridges between cysteines Cys336-Cys361, cys379-Cys432, cys391-Cys525 and Cys480-Cys488, which help create a very compact and stable structure (Lan et al (2020), nature volume 581:215-230).

RBD is a small molecule with a molecular weight in the range of 25-27kDa, depending on the expression host and the carbohydrate incorporated (Chen et al, 2017,Journal of Pharmaceutical Sciences 106:1961-1970) that is linked primarily to asparagine N331 and N343.

Strategies for SARS-Cov-2 vaccines include inactivating the virus, genetic constructs containing viral genetic material integrated into the adenovirus or in the form of messenger RNA, and vaccines based on subunits or fragments of viral proteins expressed in genetically modified hosts. In this case, the preferred molecule is the S protein (also known as spike protein) or a fragment of its structure, namely RBD. Their main advantage is their safety, as this strategy is closer to that of many vaccines being used, however, its main challenge is to achieve an immune response sufficient to prevent viral infection.

To date (21 months 9 of 2020), 149 SARS-CoV-2 candidate vaccines have been evaluated preclinically and 38 are in clinical trials. Of these 38 vaccines, at least 13 candidate vaccines (5 in clinical trials, 8 in preclinical studies) were specific for RBD (covd-19 candidate vaccine DRAFT profile (DRAFT land cope) -21 in 9 months 2020).

These vaccines include RBD (world wide web site: clinicaltrias/ct 2/show/NCT04466085term = NCT04466085& draw = 2& rank = 1, consulted at month 8, 17 in 2020) adsorbed on alumina at high concentrations of up to 50 micrograms per dose. Other candidate vaccines use RBD proteins comprising amino acid residues 319-545 expressed in baculovirus and insect cells, purified and formulated using aluminum hydroxide as an adjuvant. (Yang J et al (2020) Nature volume 586: 572-592). RBD in its monomeric form was also used in animal experiments, adsorbed on alumina, demonstrating that it can induce neutralizing antibodies without producing antibody-dependent enhancement (Zang j. Et al (2020) biorxiv 2020.05.21.107565).

None of the above approaches the present invention. The inventors of the present invention utilized RBD structures to obtain RBDs covalently conjugated to carrier proteins. These conjugates may be obtained from any fragment comprising the 333-527 sequence (SEQ ID NO 2) or an extension thereof.

Surprisingly, the immune response elicited against these conjugates was stronger than that elicited by unconjugated monomeric RBD (measured in virus neutralization assay using SARS-CoV-2 and ACE 2-receptor binding inhibition assay) in terms of its kinetics and its virus neutralization ability. These are key features in the pandemic scenario caused by SARS-CoV-2. The vaccine compositions described in the present invention elicit an anti-RBD IgG antibody response at day 7 post-immunization, wherein the cellular response is polarized to Th1 mode, characterized by induction of ifnγ; thus, in this case, no immunopathological effects reported for coronavirus vaccines inducing Th2 patterns are expected to occur.

One weakness of immunity obtained after coronavirus infection is that it does not last for a long time. The vaccine compositions described herein elicit CD8 ⁺ 、CD4 ⁺ And T cell memory responses, particularly lymphocytes specific for ifnγ -producing RBDs.

Notably, prior to the present invention, no technical or scientific publications have described covalent conjugates of RBD with carrier proteins obtained by chemical means, nor vaccine compositions based on such conjugates.

Disclosure of Invention

One embodiment of the present invention is directed to a covalent conjugate comprising a SARS-CoV-2 Receptor Binding Domain (RBD) and a carrier protein. These conjugates are characterized in particular in that the ratio of RBD-carrier proteins is preferably in the molar range of 1-8 RBD units per carrier protein, although conjugates with up to 13 RBD units are also available. The carrier protein may be selected from the group comprising tetanus toxoid, diphtheria toxoid and diphtheria toxin mutant CRM 197. The immune effect achieved by conjugation with tetanus toxoid can also be produced by conjugation with other carrier proteins, and thus the effect of the invention is not limited to the use of tetanus toxoid.

RBD antigens for conjugation may have any of the amino acid sequences 319-541 (SEQ ID NO: 1), 333-527 (SEQ ID NO: 2), 328-533 (SEQ ID NO: 3). In particular SEQ ID No. 1 can also be present in dimeric form. The RBD antigen can be produced in a host selected from the group consisting of: mammalian cells (preferably non-human), insect cells, bacteria and yeast.

Another embodiment of the invention includes a vaccine composition that induces a protective immune response against SARS-CoV-2 by a covalent conjugate consisting of a SARS-CoV-2 Receptor Binding Domain (RBD) and a carrier protein. These vaccine compositions may also include an adjuvant selected from the group comprising any inorganic salts such as aluminium hydroxide, aluminium phosphate and calcium phosphate. The conjugates of the vaccine composition have RBD concentration ranging from 1-30 μg per dose, while the adjuvant is in the concentration range of 200-1500 μg per dose. These compositions also comprise suitable pharmaceutical excipients.

Another embodiment of the invention relates to a method for obtaining a covalent conjugate comprising the steps of: a) Functionalization of the carrier protein for introduction of a thiophilic group; b) Covalent conjugation of the carrier protein to the RBD, and C) purification. The method may further comprise the step of reducing the RBD dimer in situ prior to step a, wherein SEQ ID No. 1 is in its dimer form (fig. 1). In addition, the process may include a further step of RBD N-terminal thiolation prior to step A, wherein SEQ ID NOs 1-3 (FIG. 2) are used. The thiophilic group introduced in step a of the process is selected from the group comprising: maleimides, bromoacetyl groups, vinyl sulfones, acrylates, acrylamides, acrylonitriles and methacrylates.

Another embodiment of the present invention relates to the use of the above vaccine composition for preventing SARS-CoV-2 virus infection. It particularly includes the use of the vaccine compositions described herein when a neutralizing antibody response is desired.

Finally, another embodiment of the invention includes the use of the vaccine composition described above to induce an early IgG antibody response against SARS-CoV-2 using an intramuscular immunization protocol (including 1-3 injections, ranging from 1-30 μg RBD).

The present invention now provides in a first aspect a covalent conjugate comprising a SARS-CoV-2 Receptor Binding Domain (RBD) and a carrier protein.

In a preferred embodiment of the covalent conjugate of the invention, said carrier protein is selected from the group comprising: tetanus toxoid, diphtheria toxoid, and diphtheria toxoid mutant CRM197 (fig. 3 and 4).

In a preferred embodiment of the covalent conjugates of the present invention, the molar ratio of RBD-carrier protein is in the range of 1 to 8 RBD/carrier protein (FIG. 5).

In a preferred embodiment of the covalent conjugate of the invention, the RBD is selected from the group comprising: SEQ ID NOS 1, 2 and 3.

In a preferred embodiment of the covalent conjugates of the invention, the RBD of SEQ ID NO. 1 is used in its dimeric form.

In a preferred embodiment of the covalent conjugates of the invention, the RBD is produced in a host selected from the group comprising: mammalian cells (preferably non-human), insect cells, bacteria and yeast.

In another aspect, the invention provides a vaccine composition comprising a covalent conjugate of the invention as described above. The vaccine composition is preferably used to induce an immune response against SARS-CoV-2.

In a preferred embodiment of the vaccine composition of the invention, the vaccine composition further comprises an adjuvant selected from the group comprising or consisting of: aluminum hydroxide, aluminum phosphate and calcium phosphate.

In a preferred embodiment of the vaccine composition of the invention, the conjugate is present in a concentration in the range of 1-30 μg RBD per dose.

In a preferred embodiment of the vaccine composition of the invention, the concentration of adjuvant ranges from 200 to 1500 μg per dose.

In a preferred embodiment of the vaccine composition of the present invention, the vaccine composition further comprises a suitable pharmaceutical excipient.

In another aspect, the present invention provides a method of preparing a covalent conjugate of the invention as described above, the method comprising the steps of: providing a carrier protein and an RBD, wherein the RBD may be in monomeric or dimeric form, functionalizing the carrier protein by introducing a thiophilic group, covalently conjugating the carrier protein to the RBD, and purifying the resulting conjugate.

In a preferred embodiment of the method for preparing the covalent conjugates of the invention, wherein RBD dimers are used, the method comprises an additional step of reducing the RBD dimers, preferably in situ, prior to their conjugation to the carrier protein, preferably prior to functionalizing the carrier protein by introducing a sulfur-philic group.

In a preferred embodiment of the method of preparing the covalent conjugates of the present invention, the RBD of any one of SEQ ID NO:1-3 may be used, most preferably SEQ ID NO:1 is used as RBD.

In a preferred embodiment of the method of preparing a covalent conjugate of the invention, the introduced thiophilic group is selected from the group comprising or consisting of: maleimide, bromoacetyl, vinyl sulfone, acrylate, acrylamide, acrylonitrile, and methacrylate.

In another aspect, the present invention provides a conjugate obtained by the above-described method of preparing a covalent conjugate of the invention.

In another aspect, the invention provides the use of the vaccine composition of the invention for preventing SARS-CoV-2 virus infection, in particular for preventing a disease caused by SARS-CoV-2 virus infection.

In another aspect, the invention provides a method of preventing a disease caused by a SARS-CoV-2 viral infection comprising administering to a subject a therapeutically effective dose of a vaccine composition of the invention as described above.

Preferably, in the use of preventing infection or method of preventing disease according to the invention, the use or method is for preventing a SARS-CoV-2 virus infection or a disease caused by a SARS-CoV-2 virus in a subject in need of a neutralizing antibody response after receiving two doses of the vaccine composition or 2 doses of the vaccine composition.

In a preferred embodiment of the use and method for preventing infection or disease according to the invention, the use or method is to induce a SARS-CoV-2 antibody response by applying 1 to 3 doses of an intramuscular vaccination regimen. Preferably, in one predetermined vaccination agent according to the invention, the amount of RBD in a dose is between 1 and 30 μg.

Drawings

FIG. 1 site-selective conjugation scheme of SARS-Cov-2 Receptor Binding Domain (RBD) to Tetanus Toxoid (TT) activated with a thiophilic maleimide group. Conjugation occurs at the free thiol group of Cys538, which is spatially remote from the receptor binding motif (represented in red), and therefore, it does not affect the antigenicity of RBD.

FIG. 2N-terminal selective conjugation scheme of SARS-Cov-2 Receptor Binding Domain (RBD) to Tetanus Toxoid (TT) activated with a thiophilic maleimide group. The N-terminal thiolation of RBD is performed with a novel (internally developed) mercaptoacetyl-pyridylaldehyde reagent that selectively modifies the N-terminal amino group. The N-terminal residue is spatially remote from the receptor binding motif (indicated in red) and therefore does not affect the antigenicity of RBD.

FIG. 3 is a graph of RBD conjugates based on RBD (319-541) conjugated at Cys538 using A) tetanus toxoid, B) diphtheria toxoid, or C) cross-reactive material 197 (CRM 197) as carrier protein.

FIG. 4 is a graph based on RBD conjugates of RBDs (328-533) conjugated at the N-terminus using A) tetanus toxoid, B) diphtheria toxoid, or C) cross-reactive substance 197 (CRM 197) as carrier protein.

FIG. 5. Representative RBD-TT conjugates with an average of 2, 4 and 6 RBDs per unit tetanus toxoid. Conjugates with an average of 8, 10 or 13 RBD units were also obtained.

FIG. 6.HPSEC Superdex 75 is a chromatogram showing the reduction of RBD dimer (SEQ ID NO: 1) to RBD monomer and comparison with a reference spectrum of RBD monomer.

FIG. 7 10% SDS-PAGE of the native form of RBD and reduced RBD derived from RBD dimer (SEQ ID NO: 1). R: the sample is incubated in a reducing sample buffer and then applied to the gel. NR: the sample is applied in a non-reducing sample buffer.

FIG. 8 antigenicity of monomers obtained by reduction of RBD dimer (SEQ ID NO: 1) with tris (2-carboxyethyl) phosphine (TCEP) compared to antigenicity of natural monomers and dimers.

FIG. 9 HPSEC Superdex 200 chromatogram of purified RBD-TT 2 and 3 conjugates (example 2) compared to the chromatogram of tetanus toxoid.

FIG. 10 recognition of RBD (319-541) -TT conjugates by ELISA (A) and dot blot analysis using anti-RBD polyclonal antibodies (B).

FIG. 11 and Al (OH) ₃ In contrast to the RBD formulated in the prior art, in the case of the RBD used in Al (OH) ₃ Formulated or notIn Al (OH) ₃ Kinetics of anti-RBD IgG antibodies induced by RBD-TT conjugates formulated in (a) after vaccination on day 0 and day 14. Asterisks indicate the significant difference (p.ltoreq.0.05) between groups at each time.

FIG. 12 is a schematic illustration of the use of Al (OH) ₃ Formulated in the middle or not in Al (OH) ₃ Kinetics of anti-TT IgG antibodies induced by RBD-TT conjugates formulated at day 0 and day 14 post-vaccination.

FIG. 13 and Al (OH) ₃ Compared to the RBD formulated in the above, the RBD was used in mice (in Al (OH) ₃ Formulated in (C) or not in Al (OH) ₃ Vaccine compositions of RBD-TT conjugates) were tested for inhibition of RBD-ACE2 binding in day 28 induced antibody dilutions at day 0 and day 14 immunized).

FIG. 14 and Al (OH) ₃ In contrast to the RBD formulated in the prior art, the RBD is prepared from two doses of the compound in Al (OH) ₃ Formulated in the middle or not in Al (OH) ₃ Serum from mice immunized with the RBD-TT conjugate prepared in (C) was active against SARS-CoV-2 on day 28. Asterisks indicate significant differences (p<0.05)。

FIG. 15, use in Al (OH) as determined by quantitative ELISA ₃ RBD-TT formulated in (A) or with placebo (Al (OH) ₃ ) Production of ifnγ, IL4 and IL17A in spleen cells of immunized mice. According to Tukey test, asterisks indicate significant differences (p <0.05)。

FIG. 16 is a graph showing that two doses of Al (OH) are used ₃ The memory cell response induced in mice immunized with the RBD-TT conjugate. (A) CD8 ⁺ CD44 ⁺⁺ T lymphocytes, (B) ifnγ -producing CD 8T lymphocytes, (C) CD4 ⁺ CD44 ⁺⁺ Memory T lymphocytes and (D) ifnγ -producing CD 4T lymphocytes. RBD/RBD: groups receiving two doses (T0, T14) of RBD-TT and the extracted lymphocytes were stimulated with RBD in vitro. alum/RBD: groups that received two doses of (T0, T14) alum and extracted lymphocytes were stimulated with RBD in vitro.

FIG. 17.HPSEC Superdex 75 is a chromatogram showing the selective thiolation of the N-terminal residue of RBD monomers (SEQ ID NO: 3) as compared to a reference profile of RBD monomers.

FIG. 18 (A) HPSEC Superdex 75 chromatogram showing conjugate of RBD monomer thiolated at the N-terminal residue (SEQ ID NO: 3) (upper panel), 16 h reaction mixture of RBD-TT 4 (middle panel) and purified conjugate of RBD-TT 4 (lower panel). (B) HPSEC Superdex 200 chromatogram of RBD-TT 4 purified conjugate compared to tetanus toxoid.

Identification of RBD (328-533) -TT conjugates by ACE-2 receptor (a) by ELISA assay and (B) by analysis of anti-RBD polyclonal antibodies (by dot blot assay).

FIG. 20 anti-RBD IgG antibodies induced on day 14 (T42) after immunization with conjugate vaccine on day 0 and day 28 in phase II clinical trial (19-80 y/o) and phase I/II clinical trial (3-18 y/o). PCP: a panel of sera from pediatric convalescence patients.

FIG. 21 anti-RBD IgG from saliva samples of vaccinated or non-vaccinated subjects

Detailed Description

As used herein, the term "SARS-CoV-2" refers to Severe Acute Respiratory Syndrome (SARS) coronavirus 2 (SARS-CoV-2), a causative virus of coronavirus disease 2019 (COVID-19). Detection of SARS-CoV-2 positive cases can be based on detection of viral RNA sequences by NAAT, such as real-time reverse transcription polymerase chain reaction (rRT-PCR), as confirmed by nucleic acid sequencing, if necessary. Currently targeted viral genes include N, E, S and RdRP genes. The terms "SARS-CoV-2 disease" and "COVID" are used interchangeably herein to refer to a viral infectious disease caused by severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). Common symptoms of covd-19 include fever, cough, and shortness of breath. Muscle pain, sputum production and sore throat are less common. Most cases lead to mild symptoms, while some cases develop severe pneumonia and multiple organ failure. Infection is typically transmitted from one person to another by respiratory droplets produced during coughing. It may also be propagated by touching the contaminated surface and then touching the face of the person.

As used herein, the term "Receptor Binding Domain (RBD)" refers to the Receptor Binding Domain (RBD) of the coronavirus spike (S) protein of a coronavirus and includes a portion of the coronavirus spike (S) protein that is involved in the attachment of the virus to a receptor on a cell of a subject and subsequently into the cell. The cellular receptor may be an angiotensin converting enzyme 2 (ACE 2) receptor. Preferably, the RBD comprises or consists of the amino acid sequences of SEQ ID NOS.1-3. In the definition of RBD, RBD is also contemplated as an antigenic portion of the amino acid sequence of SEQ ID NO: 1-3. The RBDs described herein can be modified, wherein 1-100, preferably 1-50, more preferably 1-10 amino acid residues are added, substituted or deleted from the amino acid sequence of SEQ ID NO:1-3 or an antigenic portion thereof, preferably wherein said modified RBD binds to a product of an immune response, preferably an antibody, which is elicited when a subject is immunized with a conjugate as described herein, wherein the RBD of said conjugate comprises or consists of the amino acid sequence of SEQ ID NO: 1-3. Thus, the term "RBD" includes products (preferably antibodies) having 80%, preferably 90%, more preferably 95% sequence identity to SEQ ID NOS: 1-3 and binding to an immune response, which is elicited when a subject is immunized with a conjugate as described herein, wherein the RBD of the conjugate comprises or consists of the amino acid sequences of SEQ ID NOS: 1-3.

In some aspects of the invention, the term "Receptor Binding Domain (RBD) of a coronavirus spike (S) protein" refers only to the RBD portion of the intact coronavirus spike (S) protein.

The term "spike (S) protein" or equivalent term "spike (S) glycoprotein" refers to a coronavirus S protein consisting of an S1 subunit (N-terminal head) and an S2 subunit (C-terminal stem). The S1 subunit mediates viral attachment and entry through its N-terminal S1A domain (containing sialic acid, a viral attachment factor) and its C-terminal Receptor Binding Domain (RBD), which binds the SARS ACE2 receptor. The S2 subunit is more conserved, mediating fusion of the virus with the host cell by Fusion Peptide (FP) and two heptad repeat (HR 1 and HR 2). Binding of the SARS-CoV S protein RBD to human ACE2 and CLEC4M/DC-SIGNR receptors results in internalization of the virus into the endosome of the host cell.

As used herein, the term "carrier protein" refers to an immunogenic protein to which an antigen, such as a protein, oligosaccharide or polysaccharide, can bind. When bound to a carrier, the bound molecule may become more immunogenic. Covalent attachment of the molecule to the carrier enhances immunogenicity and T cell dependence.

As used herein, the term "protein" refers herein to a series of amino acid residues, also referred to as "polypeptides," that are linked to each other by peptide bonds between the α -amino and carboxyl groups of adjacent residues. The terms "protein" and "polypeptide" refer to polymers of amino acids, including modified amino acids (e.g., phosphorylated, glycosylated, etc.), and amino acid analogs, regardless of their size or function. "proteins" and "polypeptides" are generally used to refer to relatively larger polypeptides, while the term "peptide" is generally used to refer to small polypeptides, but these terms are used in the art to overlap. In the present specification, the terms "protein", "polypeptide" and "peptide" are completely interchangeable.

It should be understood that the proteins comprising the (RBD) antigens of the invention may differ from the exact sequences illustrated and described herein. Thus, the present invention contemplates deletions, additions and substitutions of the indicated sequences, so long as the sequences function in accordance with the methods of the present invention. Particularly preferred substitutions in this regard are generally conservative in nature, i.e., those that occur within a family of amino acids. For example, amino acids are generally divided into four families: (1) acidic- -aspartic acid and glutamic acid; (2) basic- -lysine, arginine, histidine; (3) Nonpolar-alanine, valine, leucine, isoleucine, proline, phenylalanine, methionine, tryptophan; and (4) uncharged polarity- -glycine, asparagine, glutamine, cysteine, serine, threonine, tyrosine. Phenylalanine, tryptophan, and tyrosine are sometimes classified as aromatic amino acids. It can be reasonably predicted that isoleucine or valine alone replaces leucine or the reverse; substitution of glutamic acid for aspartic acid or vice versa; replacement of threonine with serine or vice versa; or similar conservative substitutions of amino acids with structurally related amino acids will not have a significant impact on biological activity. Thus, proteins having substantially the same amino acid sequence as shown and described but with a small number of amino acid substitutions that do not substantially affect the immunogenicity of the protein are within the scope of the invention. At least 90%, preferably at least 95%, 96%, 97%, 98% or 99% sequence identity over the full length of the RBD protein is considered to be a functional variant of the RBD protein of SEQ ID NO. 1-3 and is useful in aspects of the present invention. The term "% sequence identity" is defined herein as the percentage of nucleotides or amino acids in a nucleic acid sequence or amino acid sequence that are identical to the nucleotides or amino acids in the nucleic acid sequence or amino acid sequence, respectively, of interest after aligning the sequences and optionally introducing gaps, if necessary, to obtain the maximum percentage of sequence identity. Methods and computer programs for alignment are well known in the art. Sequence identity is calculated over substantially the entire length, preferably the entire (full) length, of the amino acid sequence of interest. The skilled person will understand that consecutive amino acid residues in one amino acid sequence are compared to consecutive amino acid residues in another amino acid sequence.

As used herein, the term "tetanus toxoid" refers to a well-known tetanus toxoid peptide, which represents an epitope of residues 830-844 of tetanus toxin. This sequence has been shown to bind to multiple HLA-DR alleles and has been described as being universally immunogenic. The amino acid sequence is QYIKANSKFIGITEL.

As used herein, the term "diphtheria toxoid" refers to an inactivated exotoxin (a 535 amino acid single polypeptide chain consisting of two subunits linked by disulfide bonds) secreted by corynebacterium diphtheria (Corynebacterium diphtheriae). Diphtheria toxoid is produced worldwide in a standard manner; in the united states, production and testing procedures are specified in federal regulations.

As used herein, the term "diphtheria toxoid mutant CRM197" refers to a nontoxic mutant of diphtheria toxin, typically used as a carrier protein for polysaccharides and haptens, to render them immunogenic. A single G- > A transition in the wild-type diphtheria toxoid sequence results in glycine-52 substitution with glutamic acid (Giannini et al 1984Nucleic Acids Res.12 (10): 4063-4069),

as used herein, the term "covalent" refers to a chemical bond where two atoms share one or more pairs of electrons holding them together.

As used herein, the term "covalent conjugate" refers to a compound in which an antigen polypeptide is covalently linked to a carrier protein.

As used herein, the term "covalent conjugation" refers to the step of preparing a conjugate by chemical reaction.

As used herein, the term "vaccine" includes compositions of antigenic moieties, typically consisting of a modified live (attenuated) or inactivated infectious agent or some portion of an infectious agent, most commonly administered in vivo with an adjuvant to generate active immunity. The present invention provides an immunogenic composition comprising a conjugate as described above in a pharmaceutically acceptable carrier. Such a carrier may be an aqueous liquid or an aerosol composition.

As used herein, the term "agent" refers to the amount or measured amount of a conjugate or composition of the invention that is administered or recommended to be administered at a particular time.

As used herein, the term "adjuvant" includes one or more compounds that, when used in combination with a particular vaccine antigen in a formulation, enhance or otherwise alter or modify the immune response generated. Preferably, the adjuvant is alum (aluminium salt) such as aluminium hydroxide.

As used herein, the term "pharmaceutical excipient" refers to substances such as adjuvants, carriers, pH adjusting agents and buffers, tonicity adjusting agents, wetting agents, preservatives and the like. Vaccine excipients are described, for example, in government regulations such as the european pharmacopoeia and the united states 9CFR, and in manuals such as the following: the Handbook of Pharmaceutical Excipients (R.Rowe et al Pharmaceutical press 2012,ISBN 08571 10276); remington: the science and practice of pharmacy (2000, lippincot, USA, ISBN: 683306472).

As used herein, the term "in situ reduction" refers to the conversion of RBD from dimer to monomer as described herein. The reduction of the dimer is preferably carried out using tris (2-carboxyethyl) phosphine (TCEP). Preferably, the reduction is in situ, which means that the dimer is mixed with TCEP and then with the carrier protein without any intermediate purification steps.

As used herein, the term "thiolation" refers to the introduction of a thiol (SH) group into the N-terminal or N-terminal residue of an RBD. Thiolation can be achieved by reacting RBD with excess 2-mercaptoacetyl-pyridine-2-carbaldehyde followed by treatment with hydroxylamine.

As used herein, the term "functionalized" refers to the introduction of one or more thiophilic groups into the carrier protein. The thiophilic group may include maleimides, bromoacetyl groups, vinyl sulfones, acrylates, acrylamides, acrylonitriles and methacrylates. Methods for introducing one or more thiophilic groups into a protein are well known to those skilled in the art. Functionalization can be achieved, for example, by reacting the carrier protein with N-hydroxysuccinimide maleate in a suitable buffer.

In some aspects of the invention, the thiolated RBD is then reacted with one or more sulfur-philic group functionalized carrier proteins to form the conjugates of the invention. The resulting conjugate will contain 1-8 RBD units per unit carrier protein, depending on the reaction stoichiometry. The conjugation methods described for the present invention are chemoselective and residue specific. The covalent conjugates according to the invention are preferably not fusion proteins, wherein the RBD is bound to the carrier protein via peptide bonds.

As used herein, the term "administering" refers to placing a compound or composition disclosed herein into a subject by a method or route that results in at least partial delivery of the conjugate at the desired site. Pharmaceutical compositions comprising the compounds disclosed herein can be administered by any suitable route that results in effective treatment in a subject. Preferably by injection, preferably intramuscularly.

As used herein, "subject" means a human or non-human animal. Typically the non-human animal is a vertebrate, such as a primate, rodent, livestock or game animal. Primates include chimpanzees, cynomolgus monkeys, spider monkeys, and macaques, e.g., rhesus monkeys. Rodents include mice, rats, woodchuck, ferrets, rabbits, and hamsters. Animals also include armadillo, hedgehog, and camel, to name a few. Domestic animals and game animals include cattle, horses, pigs, deer, wild cattle, buffalo, feline species (e.g., domestic cats), canine species (e.g., dogs, foxes, wolves), avian species (e.g., chickens, emus, ostriches), and fish (e.g., trout, catfish, and salmon). In some embodiments, the subject is a mammal, e.g., a primate, e.g., a human. The terms "individual," "patient," and "subject" are used interchangeably herein. Preferably, the subject is a mammal. The mammal may be a human, non-human primate, mouse, rat, dog, cat, horse, cow or pig, but is not limited to these examples. Mammals other than humans can be advantageously used as subjects for animal models representing a given disorder. The subject is preferably a human. The subject may be male or female. The subject may be a subject who has been previously diagnosed or identified as having or having a condition in need of treatment, and optionally has been treated. Alternatively, the subject may be a subject who has not been previously diagnosed as having a disorder. For example, the subject may be a subject that exhibits one or more risk factors, or a subject that does not exhibit a risk factor.

A "subject in need of treatment for a particular disorder" may be a subject suffering from, diagnosed with, or at risk of developing the disorder.

As used herein, the term "preventing SARS-CoV-2 virus infection" and the term "preventing a disease caused by SARS-CoV-2 virus infection" refer to preventing or treating a disease of COVID-19, or a disease caused by SARS-CoV-2 virus or a variant thereof.

As used herein, the terms "treatment", "treatment" or "amelioration" refer to a therapeutic treatment in which the purpose is to reverse, alleviate, ameliorate, inhibit, slow or stop the progression or severity of a condition associated with a disease or disorder (e.g., cancer or inflammation). The term "treating" includes reducing or alleviating at least one side effect or symptom of a disorder, disease, or condition. Treatment is generally "effective" if one or more symptoms or clinical markers are reduced. Alternatively, a treatment is "effective" if the progression of the disease slows or stops. That is, "treatment" includes not only improvement of symptoms or markers, but also cessation or at least slowing of symptom progression or worsening as compared to what would be expected without treatment. Beneficial or desired clinical results include, but are not limited to, alleviation of one or more symptoms, diminishment of extent of disease, stabilization of the disease state (i.e., not worsening), delay or slowing of disease progression, amelioration or palliation of the disease state, remission (whether partial or total), and/or reduction in mortality, whether detectable or undetectable. The term "treatment" of a disease also includes alleviation of symptoms or side effects of the disease (including palliative treatment).

The term "effective amount" as used herein refers to the amount of vaccine antigen required to alleviate at least one or more symptoms of a disease or disorder, and relates to a sufficient amount of a pharmaceutical composition to provide a desired effect. Thus, the term "therapeutically effective amount" refers to an amount of vaccine antigen that is sufficient to produce a particular effect when administered to a typical subject. An effective amount, as used herein in various contexts, also includes an amount sufficient to delay the progression of a disease symptom, alter the progression of a symptomatic disease (e.g., without limitation, slow the progression of a disease symptom or its severity), or reverse a disease symptom. Thus, it is often not feasible to specify an exact "effective amount". However, for any given situation, a suitable "effective amount" may be determined by one of ordinary skill in the art using only routine experimentation. An effective amount preferably elicits a neutralizing antibody response in a subject.

As used herein, the term "therapeutically effective amount" refers to an amount of a therapeutic agent for treating, ameliorating, counteracting, inhibiting or preventing a desired disorder or condition, or exhibiting a detectable therapeutic or prophylactic effect. The precise effective amount required by a subject will depend on the size and health of the subject, the nature and extent of the disease, and the therapeutic agent or combination of therapeutic agents selected for administration. The therapeutically effective amount for a given situation can be determined by routine experimentation.

The term "neutralizing antibody response" refers to the production of antibodies in a subject that bind to the RBD of a foreign protein, such as SARS-CoV-2, and reduce or attenuate its activity. For example, the activity of the foreign protein may be reduced by a detectable amount, e.g., 10%, 25%, 50%, 75% or 100% (i.e., completely inactivated), as compared to the activity of the foreign protein in the absence of the neutralizing antibody response or prior to eliciting the neutralizing antibody response. The activity of the foreign protein will depend on the foreign protein, which can be determined by any method known in the art.

As used herein, the term "vaccination" refers to administration of a vaccine to induce a neutralizing antibody response by the immune system of a recipient to produce protection against disease.

The term "pharmaceutically acceptable" is used herein to refer to those compounds, materials, compositions, and/or dosage forms which are, within the scope of sound medical judgment, suitable for use in contact with the tissues of human beings and animals without excessive toxicity, irritation, allergic response, or other problem or complication, commensurate with a reasonable benefit/risk ratio.

Method for obtaining RBD antigen

The coding sequence for the RBD protein is synthesized and subcloned in a suitable expression vector, preferably pcDNA3.1. The RBD amino acid sequence selected is SEQ ID NO. 1-3 or an extension thereof. Constructs containing the target protein may be expressed in one of the hosts conventionally used in biotechnology (i.e., mammalian cells (CHO, HEK 293), insect cells, bacteria and yeast, preferably CHO cells).

Harvesting the expressed target protein by centrifugation and filtration; it is purified on an affinity column, preferably a Ni-Sepharose column, followed by size exclusion chromatography, preferably using Superdex 200. Purified proteins are analyzed by using suitable methods such as SDS-PAGE, HPSEC, and MS to determine molecular size, purity, identity, and amino acid sequence, as well as other molecular characteristics.

To obtain a covalent conjugate with a carrier protein, the present inventors utilized the structure of RBD, which is a globular protein containing 195 amino acids (sequence Thr333-Pro527, SEQ ID NO: 2). The sequence contains four intramolecular disulfide bonds between cysteines (Cys 336-Cys361, cys379-Cys432, cys391-Cys525, and Cys480-Cys 488), resulting in a very compact and stable structure. This sequence constitutes a biologically relevant structure for the conjugation of RBDs, since it contains the four immunodominant epitopes described for the molecule, as well as the receptor binding motif. These conjugates may be obtained from any fragment comprising the 333-527 sequence or an extension thereof.

Furthermore, the gene construct for producing RBD may comprise an extension at one or both ends of the 333-527 sequence, or an extension at the N-terminus of any of the amino acids from 333 to 300, or an extension at the C-terminus in the amino acid region of 527-560. By extending the sequence to include one of the natural amino acids considered active (e.g., cysteine 538), it is possible to activate one of the termini without affecting the biologically relevant structure, by the genetic construct itself, in particular. Another solution consists in introducing a reactive functional group at one end; an example of this is the functionalization of the thiol group of the N-terminal amino acid, for example on arginine 328 of the 328-533RBD sequence (SEQ ID NO: 3).

The amino acid sequence of the target protein from SEQ ID NO. 1 contains 9 cysteines, 8 of which participate in 4 intramolecular disulfide bonds (Cys 336-Cys361, cys379-Cys432, cys391-Cys525 and Cys480-Cys 488), which results in a very compact and stable structure. During purification of the RBD and in the presence of air (mild oxidation conditions), the RBD of SEQ ID NO:1 can dimerize by forming disulfide bonds between the two free cysteines at position 538 of the two RBD molecules. However, if the RBD is maintained in an atmosphere of an inert gas (i.e., nitrogen or argon), the cysteine 538 does not react, and the RBD maintains its monomeric form, and thus, it may participate in a chemical reaction with the thiophilic group.

Method for obtaining covalent conjugates of RBD and carrier proteins

The carrier protein may be selected from the group comprising: tetanus toxoid, diphtheria toxoid, and diphtheria toxin mutant CRM197, or any other protein that performs the same function in a human vaccine. Methods for obtaining and characterizing these carrier proteins can be found in the available literature.

The conjugation methods described for the present invention are chemoselective and residue specific. The method is divided into three stages. The first stage (A) involves functionalizing the carrier protein to introduce thiophilic groups, preferably maleimides, and any known thiophilic groups, namely bromoacetyl, vinyl sulfone, acrylates, acrylamides, acrylonitriles and methacrylates, may be used. Functionalization can be achieved by using N-hydroxysuccinimide maleate in dimethyl sulfoxide (DMSO) with the protein in a suitable buffer at a molar ratio of 100-200. The functionalized proteins were purified by diafiltration using a membrane having an MWCO value suitable for the protein under purification, and the extent of functionalization was determined by using the modified Ellman method.

Stage (B) comprises conjugating the RBD with the functionalized carrier protein in a suitable buffer, adding them to the reaction mixture in a mass ratio of 0.2-9.4RBD to carrier protein (w: w); the mixture was gently stirred at 5.+ -. 3 ℃ under an inert gas atmosphere for 4-18 hours. The remaining thiophilic groups are blocked by adding an appropriate amount of cystamine.

Stage (C) involves purifying the obtained conjugate, which can be achieved by diafiltration using a membrane with a MWCO value suitable for the carrier protein.

Conjugation can be achieved by using the RBD of SEQ ID NO. 1 in monomeric and dimeric form. A further step is introduced prior to step (a) comprising the reduction of the intermolecular disulfide bridge in RBD dimers with a disulfide bond reducing agent, preferably dithiothreitol (DDT) or tris (2-carboxyethyl) phosphine (TCEP), at a concentration in the range of 125 μm-420 μm under mild reducing conditions, at a temperature in the range of 0 to 23 ℃ in 5-20 minutes. These conditions specifically selectively cleave the bridge, but do not affect the other four intramolecular disulfide bridges described above. The reduction of the dimer to monomer can be verified by HPSEC, while the retention and antigenicity of the four intramolecular disulfide bridges are checked by SDS-PAGE and indirect ELISA tests, respectively.

Another embodiment of the present invention includes the further step of thiolating the N-terminal residue of the RBD prior to step A. This procedure requires reaction with an excess of 2-mercaptoacetyl-pyridine-2-carbaldehyde (20-50 equivalents relative to RBD) at 23-37℃for 12-48 hours followed by washing and treatment with an excess of hydroxylamine at ambient temperature for 1-5 hours.

The resulting conjugate will contain 1-8 RBD units per unit carrier protein, depending on the reaction stoichiometry.

Vaccine composition and route of administration

SARS-CoV-2 vaccine based on covalent conjugate of receptor binding domain and carrier protein is administered via intramuscular or subcutaneous route at RBD dose of 1-30 μg, preferably 5-25 μg. These vaccine compositions may contain any mineral salt as an adjuvant, including but not limited to aluminium hydroxide, aluminium phosphate and calcium phosphate, in a dose ranging from 200 to 1500 μg, preferably 500 to 1000 μg. The vaccine composition comprises a suitable pharmaceutical excipient with an adjustable pH, such as phosphate buffer in a concentration range of 3.0 to 7.0mM, isotonic solution (e.g. sodium chloride) in a concentration range of 50 to 150mM, and a preservative, such as thimerosal, phenol, 2-phenoxyethanol, methylparaben, formaldehyde, m-cresol or other methyl and propyl p-hydroxybenzoates, preferably thimerosal.

Preferably, these vaccine composition formulations are administered according to a regimen of 1 to 3 doses, preferably every 7 to 28 days, more preferably every 14 to 28 days, more preferably every 21 to 28 days. Preferably, there is a spacing of at least one to three weeks, preferably a spacing of at least two weeks, between consecutive administrations. The single dose for administration preferably comprises RBD in an amount of 1 to 30 μg. A container (such as a syringe bottle) may include multiple doses for vaccination of multiple subjects. Preferably from about 0.05 to about 1mL per dose, preferably from about 0.3 to about 0.5mL per dose, and most preferably about 0.3mL per dose. The dose may be contained in a container in concentrated or lyophilized form and may be diluted or reconstituted with a suitable injection prior to administration.

The administration is preferably intramuscular. The administration is preferably not intravascular, subcutaneous or intradermal. The vaccine compositions presented in the present invention demonstrate their superiority over vaccine compositions containing adjuvanted, unconjugated RBD; these vaccine compositions have several characteristics at the present timeThe rapidity of the eliciting response, and the high level of antibody titres as neutralizing agents for the SARS-CoV-2 virus and as blockers of RBD-ACE2 receptor interactions are critical in pandemic situations. These compositions elicit Th1 type immune responses and CD8 specific for RBD ⁺ 、CD4 ⁺ And T cells (particularly those that produce IFNγ).

Further advantageous aspects

The vaccine composition proposed by the present invention shows excellent results for clinical trials in pediatric population.

Furthermore, the vaccine composition proposed in the present invention shows a mucosal IgG response in vaccinated humans. The importance is that this induced mucosal response reduces viral transmission and its infectivity. The inventors believe this is a unique new feature in the currently available Covid-19 vaccine.

The RBD structure currently proposed is believed to have important advantages as part of a complete spike protein vaccine, as the complete spike protein vaccine shows important adverse events such as myocarditis and pericarditis. These side effects are associated with the carboxy region of the spike protein. This region is not present in the RBD-carrier protein conjugate vaccines currently proposed. Notably, the currently proposed vaccine compositions are well suited for pediatric use, as the side effects of the mentioned complete spike protein vaccine are particularly severe in pediatric populations.

Preliminary results indicate that immune responses in immunosuppressed and immunocompromised subjects are highly beneficial and superior to other vaccines.

The inventors did not identify other adverse events reported for inactivated viral vaccines or adenovirus vector vaccines and the evaluation of immune responses or neutralizing antibody responses was higher than for inactivated viral vaccines.

Examples

Example 1. RBD (319-541) monomers were prepared from RBDs dimerized at Cys 538.

RBD dimer (319-541) was dissolved in PBS buffer (35 mM, pH 7.4), 0.5mM EDTA to give a final protein concentration of 5 to 10mg/mL. TCEP was added to final concentrations of 125. Mu.M to 420. Mu.M. The reaction was kept under argon for ten minutes at ambient temperature with moderate stirring.

Conversion to monomeric form and its molecular integrity were verified by HPSEC and polyacrylamide gel electrophoresis, respectively. Fig. 6 shows HPSEC spectra, which reveals that the monomer obtained by reduction has the same molecular distribution as the natural monomer. FIG. 7 (SDS-PAGE) shows: RBD monomer regenerated by reduction (lane 3) has the same migration pattern as native RBD monomer (lane 2, native conformation), in contrast to the control sample (lane 4) which was subjected to severe conditions to reduce intermolecular and intramolecular bridges, which showed slower migration.

The antigenicity of the monomers obtained by reduction was analyzed by indirect ELISA using the convalescence serum of the COVID-19 person. FIG. 8 demonstrates that RBDs regenerated by reduction are recognized as natural RBDs, whereas RBD monomers that are reduced under severe conditions break intermolecular and intramolecular disulfide bonds (total, C-), which are not recognized by the serum.

EXAMPLE 2 preparation of RBD (319-541) -tetanus toxoid conjugate

Functionalization of the carrier protein: tetanus toxoid carrier protein (5 mg/mL) in HEPES buffer (100 mm, ph 7.8) was reacted with maleimide-propionic acid N-hydroxysuccinimide ester (75 mg/mL) in DSMO (slowly instilled into the reaction mixture). The reaction was held at ambient temperature for one hour. Functionalized tetanus toxoid was purified by diafiltration with washing with PBS buffer (35 mM, pH 7.4), 5mM EDTA. The degree of functionalization is determined by the modified Ellman method.

Conjugation: the functionalized tetanus toxoid is added to the RBD solution in monomeric form or in solution reduced in situ to monomeric RBD at an RBD/TT molar ratio of 0.2-0.4. The reaction was maintained under an argon atmosphere at 5±3 ℃ for 4 to 18 hours with gentle stirring. To block the remaining maleimide groups, cysteamine hydrochloride was added at a concentration of up to 157 μm and kept stirring for 30 minutes.

Purifying: purification was achieved by diafiltration using a membrane with an MWCO value of 100kDa, while washing with PBS (6 mm, ph 7.0).

The RBD/TT ratio was determined by a combination of dot blot densitometry and colorimetry. The content and molecular size distribution of unconjugated RBD was determined by HPSEC. The molecular size and polydispersity index were determined by Dynamic Light Scattering (DLS). Table 1 shows that the molar ratio of conjugate is between 1.8mol RBD/mol TT and 6.3mol RBD/mol TT, whereas the unbound RBD content is below 15%. The molecular size distribution constant (Kd) indicates an increase in the molecular size of the conjugate compared to tetanus toxoid (kd=0.31). It was also shown that the larger the number of RBD moles incorporated in the carrier protein, the larger the relative size of the conjugate population (table 1 and fig. 9).

Table 1 physicochemical characterization of rbd-TT conjugates.

* Monomers regenerated by in situ reduction of RBD dimers

Example 3 demonstration of recognition of RBD (319-541) -tetanus toxoid conjugate by ACE2 receptor and specific antibodies

Recognition of RBD-tetanus toxoid conjugate (RBD-TT) by ACE2 receptor was analyzed by ELISA test in which plates were coated with recombinant ACE2 receptor. Samples (RBD-TT, RBD dimer-of runs 1 and 2 as positive control, hPDLvs-as negative control) were added at various concentrations (0.001, 0.004, 0.019, 0.078, 0.3125, 1.25 and 5. Mu.g/ml). After incubation, RBD-specific rabbit polyclonal serum was added followed by peroxidase conjugated anti-rabbit IgG. The reaction was visualized by the corresponding substrate and read at 405 nm.

Fig. 10A shows that two conjugate batches were recognized by ACE2 receptor and RBD dimer (positive control). Thus, it was demonstrated that in situ reduction and conjugation did not affect RBD epitopes responsible for ACE2 receptor recognition of RBD.

The antigenicity of RBD-TT was verified by dot blotting using polyclonal IgG serum specific for anti-RBD. FIG. 10B shows that at each dilution tested, the conjugate was strongly recognized by the anti-RBD specific antibody, whereas Tetanus Toxoid (TT) applied at a 1:80 dilution was not recognized. Thus, conjugation was demonstrated not to affect antibody recognition of RBD.

Example 4 RBD (319-541) -TT conjugate induced a strong antibody response in BALB/c mice.

On day 0 and day 14, BALB/c mice were immunized intramuscularly with 0.1mL of one of the following formulations:

-group 1:1 μg RBD- (319-541) -TT.

-group 2: adsorbed on 500 μg Al (OH) ₃ 1. Mu.g of RBD- (319-541) -TT.

-group 3:3 μg RBD- (319-541) -TT.

-group 4: adsorbed on 500 μg Al (OH) ₃ 3. Mu.g of RBD- (319-541) -TT.

-group 5: adsorbed on 500 μg Al (OH) ₃ 3. Mu.g of RBD- (319-541) -TT.

-group 6: placebo. PBS and 500 μg Al (OH) ₃ 。

Group 6 is a negative control formulation.

Blood was drawn on days 7, 14, 21 and 28. Animal serum was analyzed by indirect ELISA to determine anti-RBD antibody titers. The 96-well NUNC Maxisorp microtiter plate was coated with RBD (3. Mu.g/mL) in 50. Mu.L of carbonate-bicarbonate buffer (pH 9.6) and incubated at 37℃for 1 hour and then the plate was washed three times with wash solution. Subsequently, the uncoated sites were blocked with 100 μl of 5% skim milk for 1 hour at 37 ℃. After washing the plates again as described above, serum (50. Mu.L/well) diluted 1:3 in phosphate buffer (pH 7.2) in 1% BSA was added at serial dilutions, usually starting from a dilution of 1:50. Plates were incubated for 1 hour at 37℃and washed again. Next, 50. Mu.L of a dilution of peroxidase-conjugated anti-mouse IgG was added to phosphate buffer (pH 7.2), 1% BSA (1:5000), and incubated for 1 hour. After the last wash, peroxidase substrate solution (50. Mu.L/well) was added. Then incubated in the dark for 20 minutes with 50. Mu.L/well of 2NH ₂ SO ₄ The reaction was terminated. Absorbance was read at 450nm in a Multiskan EX ELISA reader (Thermo Scientific). IgG titer was defined as the serum dilution that reached four times the mean absorbance value of preimmune serum (T0) at 1:50 dilutionReciprocal of the degree. For analysis and display of the results, log10 of titer was calculated for each animal. To define the responder animals, a logarithmic titer > 1.70 was taken as the cutoff corresponding to a serum dilution > 1:50. For animals whose titer was below the detection limit of the assay, a titer value of 25 and log10 of 1.4 were set.

FIG. 11 shows the use of Al (OH) ₃ The early antibody response (on days 7 and 14 post immunization) was elicited by mid-adjuvanted RBD-TT 3 μg immunization-induced IgG responses, which were significantly stronger than those induced by the same dose of Al (OH) ₃ Early antibody responses elicited by medium adjuvanted unconjugated RBD (p<0.05). This property is due to the conjugation of RBD to carrier protein. It was also shown that 1. Mu.g of the metal is in Al (OH) ₃ The medium adjuvanted RBD-TT induced similar antibody kinetics to that induced by 3 μg unconjugated RBD, demonstrating that conjugation enhanced the response to antigen.

It was also found that the adjuvanted conjugate increased the anti-RBD antibody level compared to the same dose of non-adjuvanted formulation.

EXAMPLE 5 anti-tetanus toxoid antibody titres induced by RBD (319-541) -TT conjugates

Serum extracted from mice on day 7, day 14, day 21 and day 28 after immunization according to the method described in example 4 was used to evaluate induction of anti-TT antibodies. 96 well NUNC Maxisorp microtiter plates were coated with 100 μl of tetanus toxoid (2.5 μg/mL in PBS (pH 7.2)) and incubated overnight in a wet room at 4 ℃. The plate was washed three times with washing solution. Serum was added (100 μl/well) at various dilutions (in phosphate buffer (pH 7.2), 1% bsa). Plates were incubated for 1 hour at 37℃and washed again. Next, 100. Mu.L of anti-mouse IgG dilution conjugated to peroxidase was added to phosphate buffer (pH 7.2) at 37℃and 1% BSA (1:10000) was used for 1 hour. After the last wash, 100. Mu.L/well of peroxidase substrate solution was added and incubated in the dark for 25 minutes with 2N H ₂ SO ₄ (50. Mu.L/well) the reaction was stopped. Absorbance was read at 450nm in a Multiskan EX ELISA reader (Thermo Scientific). By converting the absorbance value into IU/ml (International Unit +.Milliliters) to determine titer; based on the serial dilutions of the standard, a four parameter logarithmic logic function was used to construct the reference curve.

FIG. 12 shows that the composition is contained in Al (OH) ₃ The formulation of the medium adjuvanted conjugate induced significantly stronger anti-TT IgG responses than (p<0.05 Unadjuvanted formulation-induced anti-TT IgG responses.

Example 6 functional activity of anti-RBD antibodies induced by RBD (319-541) -tetanus toxoid conjugate was assessed by RBD-ACE2 interaction inhibition assay.

Serum extracted from mice at day 28 after immunization of the mice according to the method described in example 4 was analyzed in an ELISA assay to determine their inhibition of RBD-ACE2 interactions. Another ELISA test was performed to analyze the anti-RBD antibody-induced inhibition of RBD-ACE2 interactions. To determine the percent inhibition of RBD-ACE2 interactions, plates coated with mouse ACE2-Fc (5 μg/mL) were blocked; human RBD-Fc, which had been incubated for 1h at 37℃with serum from mice immunized with various experimental formulations, was then added at dilutions ranging from 1:25 to 1:10000. For detection of recognition, anti-human IgG (gamma chain specific) -alkaline phosphatase conjugate diluted in SSTF-T buffer, 0.2% milk was used. After the last wash, pNPP (1 mg/mL, 50. Mu.L/well) was added to the diethanolamine buffer. Plates were incubated for 20 min in the dark and the reaction was stopped with 3M NaOH (50. Mu.L/well). Absorbance was read at 405 nm. Percent inhibition was calculated by the following formula: (1-Abs 405nm human RBD-Fc+mouse serum/Abs 405nm human RBD-Fc) 100. The maximum inhibitory concentration (IC 50) was determined by nonlinear regression using software GraphPad 7.00 (GraphPad Software, inc., san Diego, CA, USA). Figure 13 shows the inhibitory capacity of serum of mice immunized with the formulation of the invention. The adjuvanted RBD-TT formulation-induced antibodies have greater inhibition capacity than the non-adjuvanted formulation-induced antibodies. Furthermore, the inhibition capacity (IC 50) of the adjuvanted conjugates was higher than that of unconjugated formulations (RBD 3. Mu.g/Al (OH) ₃ ) Is 2 times higher than the inhibition ability (RBD-TT 1. Mu.g/Al (OH) ₃ ) And 6.5 times (RBD-TT 3. Mu.g/Al (OH) ₃ ) This suggests that RBD conjugation enhances antibody functionality even at lower doses.

Example 7. Functional activity of anti-RBD antibodies induced by formulations of RBD (319-541) -tetanus toxoid conjugates was assessed by their SARS-CoV-2 neutralization ability.

RBD-TT 3 μg/Al (OH) for testing by colorimetric assay using neutral Red ₃ And RBD 3 μg/Al (OH) ₃ SARS-CoV-2 neutralization ability of serum from immunized mice on day 28 after the first administration (example 4). Vero E6 cells were incubated in MEM supplemented with 2% fetal bovine serum, 25mM/mL L-glutamine, 2. Mu.g/mL bicarbonate, 80. Mu.g/mL gentamicin, and 5. Mu.g/mL amphotericin B. The supernatant was removed from the plate and PBS (100. Mu.L/well) at pH 7.2 containing 0.02% neutral red was added. Plates were incubated for 1 hour at ambient temperature. The solution was discarded and the cell monolayer was washed twice with sterile PBS, 0.05% Tween 20. The lysis solution (absolute ethanol: ultrapure water: glacial acetic acid, 50:49:1) was added (100. Mu.L/well). The plates were incubated for 15 minutes at ambient temperature and measured in a spectrophotometer at 540 nm. Neutralization titer is the highest serum dilution with optical density values above the cutoff. The cut-off value is the average of the optical densities of wells corresponding to the cell control divided by 2.

FIG. 14 shows that the neutralizing antibody titer induced by RBD-TT conjugate is significantly higher than that induced by unconjugated RBD (p < 0.01), demonstrating the superiority of RBD conjugation because it enhances the functionality of the induced antibodies.

Example 8 Th1 cellular immune response as determined by ifnγ induced by RBD (319-541) -tetanus toxoid conjugate.

After serum extraction on day 21 post immunization, cellular immune responses were assessed in mice immunized according to the method described in example 4. 1ug for separation in Al (OH) ₃ RBD-TT or placebo Al (OH) ₃ Spleen cells of immunized mice were and re-stimulated in vitro with RBD (5 μg/mL), as determined by quantitative ELISA. The concentration applied is 1x 10 ⁶ Individual cells/mL. After 72 hours of stimulation, the culture supernatants were assayed for IL4, IL17A and IFNγ.

FIG. 15 shows the use of 1ug RBD-TT/Al (OH) ₃ IFNγ was induced by immunization demonstrating a T cell responseTh1 polarization of (c). IL4 and IL17A were not detected, demonstrating that the conjugates did not differentiate into Th2 or Th17 pattern responses.

Example 9 RBD (319-541) -tetanus toxoid conjugate induced memory T cell response specific for SARS-CoV-2RBD protein.

On day 21 post immunization, memory T cell responses were assessed in mice immunized according to the method described in example 4. 1ug for separation in Al (OH) ₃ RBD-TT formulated in (A) or with placebo Al (OH) ₃ Spleen cells from immunized mice were incubated in RPMI 1640, 10% fetal bovine serum, 100U penicillin, 100. Mu.g/mL streptomycin, 1mM pyruvate, 50. Mu.M beta. -mercaptoethanol, and 20U/mL IL-2 for 72 hours. To activate the cells, 5. Mu.g/ml RBD was added. To block cytokine secretion, brefeldin A (BD Biosciences) was added 4 to 6 hours prior to staining. Cells were washed with PBS1X and stained with anti-CD 8, anti-CD 4, anti-CD 44 and anti-CD 220 (BioLegend) for 30 min at 4 ℃. Cells were fixed and permeabilized to facilitate intracellular staining with anti-ifnγ and anti-IL 4 (BioLegend). Cell count data was obtained on a Gallios flow cytometer (Beckman Coulter) and the results were processed with software Kaluza (Beckman Coulter).

FIG. 16 shows the use of 1 μg RBD-TT/Al (OH) ₃ Immunization of (C) resulted in RBD-specific CD4 ⁺ (C) And CD8 ⁺ (A) Memory T cells, phenotype CD44 ⁺⁺ . Immunization also increased ifnγ -producing CD8 (B) and CD4 (D) memory T cells.

EXAMPLE 10 preparation of RBD (328-533) thiolated at its N-terminal end

RBD (328-533) was treated with 2-mercaptoacetyl-pyridine-2-carbaldehyde (1-10 mM final concentration) at a final concentration of 20-200. Mu.M in 5-10mL PBS (50mM,pH 7.5,5mM EDTA). The reaction mixture was stirred at a temperature of 23-37 ℃ for a period of 12-48 h. Purification was achieved by diafiltration by washing with PBS (35mM,pH 7.4,5mM EDTA). The functionalized RBD (328-533) was concentrated to 20-200. Mu.M and treated with hydroxylamine hydrochloride (final concentration 40 mM). The reaction mixture was stirred at ambient temperature under nitrogen for 1 to 5h, the conversion determined by the Ellman method being >90%.

The level of conversion of the N-terminal residue as determined by mass spectrometry was higher than 80%. HPSEC analysis demonstrated that no aggregation occurred during the reaction and that thiolated RBD maintained its molecular size distribution (fig. 17).

Example 11. Conversion of N-terminal thiolated RBD (328-533) to RBD (328-533) tetanus toxoid conjugate.

Thiolated RBD (328-533) was conjugated to tetanus toxoid according to the procedure described in example 2.

FIG. 18A shows the HPSEC Superdex 75 chromatogram of the RBD of the reaction mixture and purified conjugate after 16h conjugation. The purified conjugate had an RBD-TT molar ratio of 1.9 and an unbound RBD content of less than 15%. HPSEC Superdex 200 chromatogram (fig. 18B) showed an increase in the molecular size of the conjugate (kd=0.27) compared to the carrier protein (kd=0.31).

The conjugates obtained from SEQ ID NO. 1 and SEQ ID NO. 3 have similar physicochemical characteristics according to the method described in example 2.

Example 12 preservation of recognition of RBD (328-533) -tetanus toxoid conjugate by ACE2 receptor and specific RBD antibodies

Recognition of RBD-tetanus toxoid conjugates by ACE2 receptor and specific anti-RBD antibodies was evaluated as described in example 3.

Figure 19A shows that RBD-tetanus toxoid conjugate is recognized by ACE2 receptor and that it is recognized in RBD positive control (RBD in the absence of tetanus toxoid). Thus, it was demonstrated that both thiolation and conjugation processes of the N-terminal residues of RBD do not affect RBD epitopes responsible for recognition of RBD by ACE2 receptors.

The antigenicity of the conjugates was verified by dot blotting using anti-RBD specific polyclonal IgG serum. FIG. 19B shows that the conjugate was strongly recognized by anti-RBD specific antibodies in all dilutions tested, whereas Tetanus Toxoid (TT) was not recognized at 1:80 dilutions. Thus, conjugation was demonstrated not to affect antibody recognition of RBD.

Example 13 rbd (319-541) -TT conjugate elicits a strong antibody response in humans, especially in pediatric populations.

Vaccine formulations comprising RBD- (319-541) -TT in alum were evaluated in clinical trials in a two dose (T0, T28 day) regimen. Clinical trial procedures for adult (stage II, 19-80 years) and pediatric populations (stage I/II, 3-18 years) are described in:https://rpcec.sld.cu/trials/RPCEC00000347-En,https://rpcec.sld.cu/trials/ RPCEC00000374-En。

FIG. 20 shows the results of specific anti-RBD IgG in serum 14 days after the second dose in two clinical trials. High levels of antibodies were produced in all age groups with a serum conversion rate of 74% in the adult population (19-80 years). Notably, children in the 12-18 year old and 3-11 year old groups reached 92.8% and 99.3% seroconversion, respectively. Furthermore, median of two pediatric groups: 50.3 (15.9; 62.0 in 12-18 years) and 99.8 (39.1; 216.8 in 3-11 years) are superior to the median of the serum panel generated with the COVID-19 convalescent children: 8.7 (3.4; 15.7).

EXAMPLE 14 RBD (319-541) -TT conjugate induces specific mucosal IgG in humans

As followshttps://rpcec.sld.cu/trials/RPCEC00000360-En) Saliva from subjects immunized with two doses (T0, 28 days) of RBD- (319-541) -TT formulation in alum and dimeric RBD (T56) in alum of booster was analyzed by an "internal" ELISA assay. RBD was used as a coating (5. Mu.g/mL) and PBS-BSA 3% as blocking agent. Saliva samples were evaluated in duplicate as pure. After the incubation step, peroxidase anti-IgG human conjugate (Sigma a6029, 1:2500) was added in an appropriate buffer. The final fluorescent reaction was induced by addition of OPD substrate. The results are expressed as absorbance values.

Figure 16 shows that vaccinated subjects elicited specific anti-RBD IgG responses in saliva.

Sequence listing

<110> Instituto Finlay de Vacunas, Centro de Inmunology

Molecular, Universidad de la Habana

<120> covalent conjugates of SARS-COV-2 receptor binding domain and carrier protein and vaccine compositions comprising the same

<130> 032020CU00

<160> 3

<170> PatentIn version 3.5

<210> 1

<211> 223

<212> PRT

<213> artificial sequence

<220>

<223> recombinant DNA technology

<400> 1

Arg Val Gln Pro Thr Glu Ser Ile Val Arg Phe Pro Asn Ile Thr Asn

1 5 10 15

Leu Cys Pro Phe Gly Glu Val Phe Asn Ala Thr Arg Phe Ala Ser Val

20 25 30

Tyr Ala Trp Asn Arg Lys Arg Ile Ser Asn Cys Val Ala Asp Tyr Ser

35 40 45

Val Leu Tyr Asn Ser Ala Ser Phe Ser Thr Phe Lys Cys Tyr Gly Val

50 55 60

Ser Pro Thr Lys Leu Asn Asp Leu Cys Phe Thr Asn Val Tyr Ala Asp

65 70 75 80

Ser Phe Val Ile Arg Gly Asp Glu Val Arg Gln Ile Ala Pro Gly Gln

85 90 95

Thr Gly Lys Ile Ala Asp Tyr Asn Tyr Lys Leu Pro Asp Asp Phe Thr

100 105 110

Gly Cys Val Ile Ala Trp Asn Ser Asn Asn Leu Asp Ser Lys Val Gly

115 120 125

Gly Asn Tyr Asn Tyr Leu Tyr Arg Leu Phe Arg Lys Ser Asn Leu Lys

130 135 140

Pro Phe Glu Arg Asp Ile Ser Thr Glu Ile Tyr Gln Ala Gly Ser Thr

145 150 155 160

Pro Cys Asn Gly Val Glu Gly Phe Asn Cys Tyr Phe Pro Leu Gln Ser

165 170 175

Tyr Gly Phe Gln Pro Thr Asn Gly Val Gly Tyr Gln Pro Tyr Arg Val

180 185 190

Val Val Leu Ser Phe Glu Leu Leu His Ala Pro Ala Thr Val Cys Gly

195 200 205

Pro Lys Lys Ser Thr Asn Leu Val Lys Asn Lys Cys Val Asn Phe

210 215 220

<210> 2

<211> 195

<212> PRT

<213> artificial sequence

<220>

<223> recombinant DNA technology

<400> 2

Thr Asn Leu Cys Pro Phe Gly Glu Val Phe Asn Ala Thr Arg Phe Ala

1 5 10 15

Ser Val Tyr Ala Trp Asn Arg Lys Arg Ile Ser Asn Cys Val Ala Asp

20 25 30

Tyr Ser Val Leu Tyr Asn Ser Ala Ser Phe Ser Thr Phe Lys Cys Tyr

35 40 45

Gly Val Ser Pro Thr Lys Leu Asn Asp Leu Cys Phe Thr Asn Val Tyr

50 55 60

Ala Asp Ser Phe Val Ile Arg Gly Asp Glu Val Arg Gln Ile Ala Pro

65 70 75 80

Gly Gln Thr Gly Lys Ile Ala Asp Tyr Asn Tyr Lys Leu Pro Asp Asp

85 90 95

Phe Thr Gly Cys Val Ile Ala Trp Asn Ser Asn Asn Leu Asp Ser Lys

100 105 110

Val Gly Gly Asn Tyr Asn Tyr Leu Tyr Arg Leu Phe Arg Lys Ser Asn

115 120 125

Leu Lys Pro Phe Glu Arg Asp Ile Ser Thr Glu Ile Tyr Gln Ala Gly

130 135 140

Ser Thr Pro Cys Asn Gly Val Glu Gly Phe Asn Cys Tyr Phe Pro Leu

145 150 155 160

Gln Ser Tyr Gly Phe Gln Pro Thr Asn Gly Val Gly Tyr Gln Pro Tyr

165 170 175

Arg Val Val Val Leu Ser Phe Glu Leu Leu His Ala Pro Ala Thr Val

180 185 190

Cys Gly Pro

195

<210> 3

<211> 206

<212> PRT

<213> artificial sequence

<220>

<223> recombinant DNA technology

<400> 3

Arg Phe Pro Asn Ile Thr Asn Leu Cys Pro Phe Gly Glu Val Phe Asn

1 5 10 15

Ala Thr Arg Phe Ala Ser Val Tyr Ala Trp Asn Arg Lys Arg Ile Ser

20 25 30

Asn Cys Val Ala Asp Tyr Ser Val Leu Tyr Asn Ser Ala Ser Phe Ser

35 40 45

Thr Phe Lys Cys Tyr Gly Val Ser Pro Thr Lys Leu Asn Asp Leu Cys

50 55 60

Phe Thr Asn Val Tyr Ala Asp Ser Phe Val Ile Arg Gly Asp Glu Val

65 70 75 80

Arg Gln Ile Ala Pro Gly Gln Thr Gly Lys Ile Ala Asp Tyr Asn Tyr

85 90 95

Lys Leu Pro Asp Asp Phe Thr Gly Cys Val Ile Ala Trp Asn Ser Asn

100 105 110

Asn Leu Asp Ser Lys Val Gly Gly Asn Tyr Asn Tyr Leu Tyr Arg Leu

115 120 125

Phe Arg Lys Ser Asn Leu Lys Pro Phe Glu Arg Asp Ile Ser Thr Glu

130 135 140

Ile Tyr Gln Ala Gly Ser Thr Pro Cys Asn Gly Val Glu Gly Phe Asn

145 150 155 160

Cys Tyr Phe Pro Leu Gln Ser Tyr Gly Phe Gln Pro Thr Asn Gly Val

165 170 175

Gly Tyr Gln Pro Tyr Arg Val Val Val Leu Ser Phe Glu Leu Leu His

180 185 190

Ala Pro Ala Thr Val Cys Gly Pro Lys Lys Ser Thr Asn Leu

195 200 205

Claims (21)

1. A covalent conjugate comprising a SARS-CoV-2 Receptor Binding Domain (RBD) and a carrier protein.

2. The covalent conjugate of claim 1, wherein said carrier protein is selected from the group comprising: tetanus toxoid, diphtheria toxoid, and CRM197.

3. The covalent conjugate according to any one of claims 1 to 2, wherein the RBD-carrier protein molar ratio is in the range of 1 to 8 units RBD/1 carrier protein.

4. A covalent conjugate according to any one of claims 1 to 3, wherein said RBD is selected from the group comprising SEQ ID NOs 1, 2 and 3.

5. The covalent conjugate according to any one of claims 1 to 4, wherein the RBD of SEQ ID No. 1 is present in its dimeric form.

6. The covalent conjugate according to any one of claims 1 to 5, wherein said RBD is produced in a host selected from the group comprising: mammalian cells, insect cells, bacteria and yeast.

7. Vaccine composition for inducing an immune response against SARS-CoV-2, characterized in that it comprises a covalent conjugate according to any one of claims 1 to 5.

8. The vaccine composition of claim 7, further comprising an adjuvant selected from the group comprising: aluminum hydroxide, aluminum phosphate and calcium phosphate.

9. The vaccine composition of claim 7, wherein the conjugate is in a concentration range of 1-30 μg per dose per RBD.

10. The vaccine composition of claim 8, wherein the adjuvant is in a concentration range of 200-1500 μg per dose.

11. The vaccine composition of claims 7 to 10, further comprising a suitable pharmaceutical excipient.

12. A process for preparing the covalent conjugate of any one of claims 1 to 5, comprising the steps of: a) Functionalizing the carrier protein to introduce a sulfur-philic group; b) Covalently conjugating the carrier protein to RBD, and C) purifying.

13. The method of claim 12, comprising the additional step of reducing the RBD dimers in situ prior to step a.

14. The method of claim 12, comprising the additional step of thiolating the N-terminus of the RBD prior to step a.

15. The method of claim 13, wherein SEQ ID NO. 1 is used.

16. The method of claim 14, wherein any one of SEQ ID NOs 1-3 is used.

17. The method of claim 12, wherein in step a, the sulfur-philic group introduced is selected from the group comprising: maleimides, bromoacetyl groups, vinyl sulfones, acrylates, acrylamides, acrylonitriles and methacrylates.

18. A conjugate obtainable by the method according to any one of claims 12 to 17.

19. Use of the vaccine composition according to any one of claims 7 to 11 for the prevention of SARS-CoV-2 virus infection.

20. Use of the vaccine composition according to any one of claims 7 to 11 for preventing SARS-CoV-2 virus infection when a neutralizing antibody response is required after two doses of the vaccine composition.

21. Use of the vaccine composition according to any one of claims 7 to 11 for inducing an antibody response against SARS-CoV-2 by the intramuscular route at a dose of 1 to 30 μg RBD according to a vaccination regimen of 1 to 3 doses.